Eye health in the future: what are the challenges for the next twenty years?

When looking ahead, it is really important to know where we have come from. This allows us to project identified trends and to reflect on the tremendous amount of change that can happen over a relatively short period. Reflect for a moment on the intensity of the debate regarding the use of intraocular lenses (IOLs) in low-income settings in the 1990s. As they were still very expensive, some insisted that aphakic correction after surgery was the best approach for these countries. The subsequent availability of low-cost IOLs made the debate irrelevant. It dramatically changed our ability to provide modern IOL cataract surgery and control cataract blindness worldwide, and it laid the basis for VISION 2020. Other dramatic changes occurred with the introduction of ivermectin for onchocerciasis and azithro-mycin for trachoma, which gave us the ability to eliminate these two devastating and previously intractable causes of blindness. Our medical management of glaucoma or of age-related macular degen-eration today is totally different from what it was 20 years ago, although there is still a long way to go. Our approach to refractive error has also altered dramatically, thanks to the recognition of its importance and the availability of high-quality, low-cost spectacles. So, given what we know about the past, what are the challenges we face in the future? Doing what we know The gap between knowledge and practice To my mind, the single biggest challenge we face – and the one which will offer by far the biggest pay-off – is the challenge of fully applying what we already know. We know how to cure cataract blindness, how to cure uncorrected refractive error, how to eliminate trachoma and onchocerciasis, and how to prevent most blindness from diabetic retinopathy. We do not need to wait for a new gene to be discovered or a new laser. Why, then, aren't we putting this knowledge into practice right now? VISION 2020 recognises that three-quarters of all blindness worldwide is either avoidable or preventable with what we currently know and it aims to bridge the existing gap between knowledge and practice. The VISION 2020 initiative emphasises disease control, but it also recognises the need for eye care to be delivered through national programmes that are tailored to individual countries. The initiative also rightly emphasises human resource development and infrastructure. However, none of this is possible without money! Non-governmental organisations and donor agencies can provide some level …

Since the prevalence of visual impairment becomes higher as people age, this combination of an increasing population and an ageing population is expected to cause a signifi cant increase in the total number of blind people. 1 Estimates of the number of people with visual impairment worldwide In 1988, the number of people who were blind (visual acuity (VA) <3/60 in the better eye) was estimated to be 37 million worldwide. By 2002-04, the latest period for which we have data (see Table 1), it was estimated to be 45 million: 8 million blind due to uncorrected refractive error and 37 million blind due to other causes. 2,3 It is thought that at least 60% of blind people are women.
Little was known in 1988 about the prevalence of low vision (VA <6/18 to 3/60). In 2002, the number of people with low vision was estimated to be 124 million worldwide, but this excluded low vision due to refractive error. 2 Owing to a lack of data from surveys, it has only very recently become possible to estimate that there are 145 million people with low vision due to refractive error. 3 This fi gure brings the overall number of people with low vision to 269 million.
In total, the number of people with visual impairment (which includes both low vision and blindness) is therefore estimated to be 314 million worldwide.

Causes of blindness
Over the last twenty years, the causes of blindness have changed in proportion and actual number. Cataract has remained the major cause of blindness globally. It is particularly important in Asia. The journal is produced in collaboration with the World Health Organization. Signed articles are the responsibility of the named authors alone and do not necessarily reflect the policies of the World Health Organization. The World Health Organization does not warrant that the information contained in this publication is complete and correct and shall not be liable for any damages incurred as a result of its use. The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned.

Supporting VISION 2020: The Right to Sight
The journal is produced in collaboration with the World Health Organization

Community Eye Health
Journal blinded by trachoma, onchocerciasis, and vitamin A deficiency have tended to decrease over the last twenty years. This is due to improvements in nutrition, water supplies, sanitation, and measles immunisation coverage, as well as to the provision of certain therapeutic medicines: ivermectin (Mectizan ® ), vitamin A, and antibiotics. Figure 1 shows the proportion of cases of blindness due to each major cause, according to the most recent estimates.

Cataract
Over the past twenty years, the major advance in the treatment of cataract has been the worldwide availability of low-cost, good-quality intraocular lenses (IOLs) since the early 1990s. Their routine use has resulted in an increase in both the quality of visual outcome for patients (as shown by population-based rapid assessment of cataract surgical services) 5 and the willingness of surgeons to perform cataract surgery at an earlier time, before blindness has developed. This is detailed in the article on page 40. There is evidence that, since the introduction of IOLs, there has been an increase in cataract surgical rates around the world, and particularly in low-income countries. 4 Two other important developments in the past twenty years have been the popularisation of phacoemulsification and the introduction of small incision cataract surgery (SICS). Both have resulted in a faster and better restoration of visual acuity. With SICS, in addition, the cost per operation is also lower.
Although it is difficult to obtain accurate figures, it is likely that the global number of cataract operations has increased from about 5 million per year in 1988 to around 15 million per year now.
Despite these overall positive developments, we should not be complacent: 17 million people are blind today because they have not yet received cataract surgery.

Trachoma
In 1988, it was estimated that 150 million children were infected; this number had fallen to approximately 84 million by 2004. 6 Similarly, the number of people blind from trachoma decreased from approximately 5 million in 1988 to 1.3 million in 2002.
The SAFE strategy for trachoma control has become widely accepted, tarsal rotation has been shown to be the preferred surgical procedure for trichiasis, and oral azithromycin has become the first-choice antibiotic for mass treatment of communities with endemic trachoma infection (as shown in the article on page 43). It is also highly likely that improvements in water supply and sanitation have significantly reduced the transmission of trachoma infection in poor rural communities in Africa and Asia. However, more investigative work is required in order to reduce recurrence after trichiasis surgery and to identify the most cost-effective strategies for the distribution of azithromycin.

Onchocerciasis
In 1988, onchocerciasis was a significant cause of blindness in many countries in Africa. This same year, however, saw important developments in the treatment of the disease: Merck & Co. had registered the microfilaricide ivermectin (Mectizan ® ) a year earlier and its Mectizan ® Donation Programme came into effect, providing Mectizan ® free of charge to individuals and communities with onchocerciasis, as shown in the article on page 43. Twenty years on, the severity of onchocerciasis infection is decreasing and the number of people developing vision loss has markedly decreased. The figures for 2007 indicate that over 50 million people are now receiving Mectizan ® on an annual basis through community-directed treatment programmes.

Childhood blindness
Although vitamin A deficiency was a wellrecognised cause of blindness in children twenty years ago, little work had been done up to that time on the magnitude and causes of childhood blindness. The article on page 46 presents an overview of the data collected and the lessons learnt over the past twenty years.
These data show marked variations according to the socio-economic status of the community. For example, vitamin A deficiency still occurs in children under five years old living in very poor families and, today, rising food prices worldwide may aggravate this situation further. Similarly, retinopathy of prematurity has emerged as a significant problem in middle-income countries and in urban centres of the developing world. The most important treatable cause of childhood blindness, however, remains untreated or poorly treated cataract, which is responsible for 5-20% of all cases.  Table 1). 3 Spectacles have generally become more available and more affordable, but in many countries there is still a need for good refraction services and for appropriate dispensing of low-cost but good-quality spectacles.

Glaucoma
During the last twenty years, work has been undertaken to develop improved definitions and classifications of glaucoma. This has allowed for better estimates to be made of the number of people with this condition. 7 It is likely that the current global estimate of 4.5 million people blind due to glaucoma actually falls short of the true figure, as many surveys do not include an assessment of visual field loss and are limited to a definition of blindness based only on visual acuity. Globally, 60 million people are likely to have one of the glaucomas and up to 8 million may be blind because of this disease. Because no simple, specific, and sensitive test exists for this condition, population-based screening cannot at present be advocated; opportunistic case detection should, however, be encouraged. Unfortunately, in many low-and middle-income countries, effective treatment for glaucoma is still out of reach: medical treatment requires the availability of affordable drugs and long-term patient compliance; surgical treatment requires patient acceptance, as well as surgical skill, experience, and the capacity for long-term follow-up. This is difficult to achieve in some settings.

Diabetic retinopathy
In 1988, there were no data on the global prevalence of diabetic retinopathy or of blindness resulting from this condition. It is now estimated that there are approximately 171 million people with diabetes worldwide. Of these people, probably 10-20% have some form of retinopathy and around 1.78 million are blind. There are now better-defined screening procedures and agreed treatment protocols based upon evidence from clinical trials. In appropriate settings, therefore, there can now be a public health approach to the control of visual loss from diabetes. 8 Age-related macular degeneration (AMD) As life expectancy increases, AMD is becoming a more important problem, not only in high-income, but also in middleincome countries (see article on page 48). In 2002, it was estimated that 3.2 million people were blind from AMD. As yet, there is no proven prevention for AMD although smoking has been shown to be an important risk factor. Various surgical procedures are being tried in selected cases and recent studies indicate that vascular endothelial growth factor (VEGF) blockers can delay or stop progression of vascular AMD (see article on page 50). In spite of promising recent developments, there is, however, no proven therapy to reverse the degenerative process in all cases and current therapies remain expensive. 9 Making a difference with VISION 2020: The Right to Sight In 1988, the WHO Prevention of Blindness (PBL) programme and the International Agency for the Prevention of Blindness (IAPB) had been in existence for ten years. Over the next decade, several important developments made it possible to conceive of a global initiative to eliminate avoidable blindness: the Mectizan ® Donation Programme was established in 1987, low-cost IOLs became available in the early 1990s, and the SAFE strategy was launched in 1996. In addition, the relationship between vitamin A deficiency and childhood mortality had already been documented.
Drawing on their experiences of costeffective eye care delivery systems in several countries in the 1980s and 1990s, including in India and The Gambia, a group of nongovernmental development organisations (NGDOs), together with the WHO, launched VISION 2020: The Right to Sight in 1999. This is a global initiative to eliminate avoidable blindness from cataract, trachoma, onchocerciasis, refractive error, vitamin A deficiency, and other causes of blindness in children by the year 2020.
The World Health Assembly has since adopted resolutions urging its member states to adopt the VISION 2020 principles. More than 90 NGDOs, agencies, and institutions, together with a number of major corporations, are now working together in this global partnership.
There is little doubt that the VISION 2020 initiative has raised awareness concerning blindness and the cost-effectiveness of available interventions. It has mobilised both government and private funding for eye care and it has generated a global publicprivate partnership working with a clearly defined focus and strategy.
Estimates of global blindness made in 2002 were 15 million lower than the projections made for this same year when VISION 2020 was launched. There is also evidence that the number of people who are blind due to onchocerciasis and trachoma has decreased, as well as evidence of increasing cataract surgical rates in many countries. Our challenge now is to build on what has been achieved and to focus resources on the poorest communities in the world. The goal of VISION 2020 is to enable all persons to receive eye care and have the right to sight -which is one of their fundamental human rights.